1. Field of the Invention
The present invention relates to a manufacturing apparatus and manufacturing method for a semiconductor device onto an amorphous-silicon film of which are grown hemispherical grains (HSGs), and more specifically to a manufacturing apparatus and manufacturing method for a semiconductor device in which watermarks do not occur on an amorphous-silicon film onto which HSGs are grown.
2. Background of the Invention
In recent years, with the shrinking of the surface area of memory cells, there has been a demand for an increase in the capacitance value of capacitive parts thereof, and for this reason investigations of such methods as applying a high-permittivity film or increasing the surface area of capacitive parts are being pursued.
To increase the surface area of a capacitor, one approach is to form a the capacitor in a three-dimensional structure. Known methods which take this approach include the method of forming a trench capacitor on a layer beneath the silicon substrate, and the method or forming a stack capacitor on a layer that is above the silicon substrate. Investigations are being made into using this stack capacitor method to increase the capacitor surface area, by making the void part of the capacitor structure in the shape of a cylinder.
One means of effectively increasing the capacitance value without the need to use microprocessing technology is a method for manufacturing a semiconductor device which is disclosed in Japanese unexamined Patent Publication (KOKAI) H8-306646, whereby hemispherical grains (HSGs) are caused to grow on an amorphous-silicon film surface during the growth thereof, thereby obtaining minute protrusions and depressions thereon.
The method of simply growing HSGs in the past will now be described, with reference made to FIG. 4. First, a silicon substrate is heated and cleaned in ammonia hydrogen peroxide solution, to remove microparticles that contaminate the surface of the amorphous-silicon surface (Step S1). The volume ratio of the mixture of ammonia, hydrogen peroxide, and water is 1:1:5, and the heated cleaning is performed for 10 minutes at a temperature of 30 to 80.degree. C.
Then, the silicon substrate, from which microparticles have been removed from the amorphous-silicon film surface, is rinsed in pure water (Step S2), after which a cleaning liquid such as chlorine hydrogen peroxide water solution or sulfur hydrogen peroxide solution is used to perform heated cleaning, thereby removing metallic impurities that contaminate the amorphous-silicon film surface (Step S3). The volume ratio of the mixture of chlorine, hydrogen peroxide, and water is 1:1:6, and the heated cleaning is performed for 10 minutes at a temperature of 30 to 80.degree. C. In the case of using sulfur hydrogen peroxide solution, and the heat cleaning is performed for 10 minutes at a temperature of 80.degree. C. to 150.degree. C.
By means of this kind of cleaning liquid for the purpose of removing metallic impurities, a chemical oxide film is formed on the surface of the amorphous-silicon film. The chemical oxide surface is formed to a thickness of 1 to 1.5 nm by the oxidizing action of the cleaning liquid. Even if an attempt is made to grow HSGs on the surface of this amorphous-silicon film onto which is formed a chemical oxide film, because the chemical oxide film inhibits the migration of silicon, HSGs do not grow. Because of this phenomenon, after rinsing the amorphous-silicon substrate onto which is formed a chemical oxide film (Step S4), it is immersed in diluted hydrofluoric acid solution having a concentration of 1% or lower, thereby removing the chemical oxide film (Step S5).
After removal of the chemical oxide film, the silicon substrate is rinsed in pure water for 10 minutes (Step S6), after which it is dried by removal of the water content from the surface thereof, using a centrifugal force type drying apparatus (Step S17). To prevent the growth of a natural oxide film on the surface of the dried amorphous-silicon film, HSGs are grown on the surface of the amorphous-silicon film immediately. Then, the capacitive film is grown, and the amorphous-silicon film surface is etched with ammonia hydrogen peroxide water cleaning solution So as to form a capacitive electrode.
Because HSGs are sensitive to contamination of the surface of the amorphous-silicon film, it is necessary to perform the proper heated cleaning and processing with dilute hydrofluoric acid solution, while taking care that the bottom layer film which causes HSG growth does not become contaminated. Contamination components which can be envisioned as affecting HSG growth on the surface of the amorphous-silicon film include air-born organic matter, a natural oxide film, and water content.
For example, in the case in which the bottom layer, such as a silicon film, is immersed in dilute hydrofluoric acid solution to remove a natural oxide film, after which the amorphous-silicon film becomes hydrophobic, even after immersion in dilute hydrofluoric acid solution and drying, there is residual water on the surface of the amorphous-silicon film. On a surface of a device that has a high aspect ratio structure, the drying at a prominent step in the surface is insufficient, so that residual water remains after drying. In particular with the method of the past in which a rotating type dryer was used to dry the surface of a amorphous-silicon film to remove water content from it, there was a tendency for residual water content to remain at such a step part. This type of residual water content encourages the local growth of a natural oxide film, thereby leading to the occurrence of watermarks. If a natural oxide film forms on the surface of the amorphous-silicon film because of watermarks or the like, HSG growth can be inhibited, there can be reduced size of the depressions and protrusions in the HSG after growth, and there can be non-uniformity in these depressions and protrusions. With a amorphous-silicon film in which these types of problems have occurred, when the amorphous-silicon film is etched by ammonia hydrogen peroxide water solution that is used for the purpose of removing microparticle contamination after formation of the capacitance film and before forming the capacitance electrode, the size of the HSG depressions and protrusions become small, so that it might not be possible to achieve a sufficient capacitance, or to achieve uniform capacitance.
Accordingly, it is an object of the present invention to provide a semiconductor device manufacturing apparatus and manufacturing method that does not cause the occurrence of watermarks on the surface of an amorphous-silicon film onto which HSG growth is done.